New Jersey Geologic Survey
DGS02-3: Ground-Water Recharge for New Jersey
Project Overview

This information is provided to compliment the FGDC-compliant metadata prepared for and provided with each data set and is not intended to replace that metadata.

Contact:

Mark French
GIS Specialist
New Jersey Geological Survey
P.O. Box 427
29 Arctic Pkwy
Trenton, NJ 08625-0420
email: mark.french@dep.nj.gov

Overview:

All geographic data were originally prepared using ESRI Arc/Info or ArcView geographic information system software (GIS). Recent Modifications and new grid data were done using ArcGIS Desktop, specifically ArcMap and Spatial Analyst. Metadata were prepared and modified using ArcCatalog. Zip compressed archive files were prepared using WinZip 8.0. Data CDs were prepared using the ISO-9660 CD file system standard and can be read by any computer and operating system with ISO-9660 compatibility.

Processing:

Recharge coverages (*cmb). Watershed management area is indicated by the two numbers after the initial "w" of the filename which corresponds to the number of the watershed management area. County is indicated by the first three letters of the filename corresponding to the first 3 letters of the County.

Each shapefile was converted or exported from a corresponding Arc/Info coverage of the same name. The "shapefiles" are composed of three constituent files: SHP file containing the geographic elements (lines, points or polygons), the SHX file containing the geographic coordinate information and the DBF file containing the data attached to each geographic element. The coverage was created through the combination and generalization of three coverages. The constituent coverages were: DEP municipalities, DEP soils (derived from SCS soil surveys and the DEP ITU coverages) and DEP 1995/97 land-use and land-cover (LULC) coverages. Prior to the combination of these coverages they were processed so as to contain data items essential for calculation of ground-water recharge:

The municipality coverage had climate factor data added as the CF item. Municipal climate factors and have been superceded by Raster (grid) generated climate factors. Average and drought climate factors were derived for 42 precipitation gages in New Jersey and neighboring states which had real or corrected records of 30 years or more, and observed and calculated evapotranspiration values for New Jersey. Using this data, both climate factors were calculated as a ratio of precipitation over potential evapotranspiration. This dimensionless number was calculated for all of the climate stations. These values were used to produce a statewide spline grid of the both average and drought values. A grid or raster better models non-discrete or continuous data such as precipitation, evapotranspiration, and climate factors. These climate factor grids were used in conjunction with the combined soil-LULC coverages to produce an average and drought climate factor for each polygon in the coverage.

Spatial Analyst's zonal statistics command was used to produce these new climate factors. It overlays grids into zones (which are delineated by coverages and shapefile polygons) which are defined by an equivalent attribute value. Descriptive statistics for the groups of grid center point falling into each zone are summarized in a database table. This table can then be linked to using the zone attribute value or copied into the coverage attribute table. In the case of climate factors, the polygon-ID was used as the zone value forcing zonal statistics to produce unique climate factors for each polygon..

Soils data had soil symbol, soil series description, hydrologic soil group, and hydric soil indicator added as the symbol, series, descriptio, hsg, and the hyd items. (Some soil coverages do not have the description data attached.). Soil coverages from the DEP GIS database were utilized. These coverages were digitized from currently published county soil surveys as part of the production of the DEP Integrated Terrain Unit Maps (ITUM). These coverages consisted of multiple components (soils, atlas sheet geology, flood-prone areas and LULC) meshed together. Some generalization of line work was made to decrease the number of sliver polygons created by the combination of these layers. The ITUMs were subsequently dismantled into their constituent parts. The soils components became the current DEP GIS soils coverages. Soil coverages contained 2 items in the associated INFO polygon attribute table (PAT): SOIL-LABEL and SOIL-INCLUSIONS. A listing of each county soil series symbols (SYMBOL), soil series names (SERIES), soil series descriptions (DESCRIPTIO), soil series hydrologic soil group (HSG), and soil series hydric soil indication (HYD) was created using downloaded information from Natural Resource Conservation Service (NRCS, formerly Soil Conservation Service (SCS)) and from published soil surveys. Each county list was converted from spreadsheet format to INFO data file and matched to the soil coverage using the SOIL-LABEL item. The two original items were then dropped.

The LULC coverage received more extensive preprocessing. Some items were dropped and some new ones added. The LULC coverages were derived from the new DEP LULC coverages. The DEP LULC coverages represent an update of the DEP LULC data. The DEP and its contractor used 1995/97 aerial photos to update the 1986 LULC data. These coverages were prepared and delivered as Watershed Management Areas (WMAs). In order to produce a county coverage, several WMA LULC coverages had to be combined and then clipped to the county boundary using the mapjoin command. Once the county coverages were produced several INFO items were dropped as they were not essential to calculation of ground-water recharge values. The DEP LULC classification had to be referenced to the NJGS LULC classification found in GSR-32 (Appendix 2). Fortunately the DEP LULC classification had anticipated this and a special classification of residential areas corresponded directly to the NJGS LULC residential classifications. A prior translation of LULC codes had been developed for rural areas. This translation was modified and updated and applied to the new DEP LULC coverages. LULC codes for other areas had to be determined or modified using the observed impervious surface percentages.

The resulting LULC coverage contains the correct LULC data for ground-water-recharge calculation. These items are: LU95, the DEP LULC code; TYPE95, the DEP LULC category description; LABEL95, a short description of the DEP LULC category; LEVEL_1, the LULC category first level descriptor; LEVEL_2, the LULC category second level descriptor; LEVEL_3, the LULC category third level descriptor, PRIMARY, the NJGS LULC primary LULC category code; SECONDARY, the NJGS secondary LULC category code (Agricultural and wilderness areas); MAJOR, the NJGS LULC code; DESC, NJGS LULC category description; IS, percentage of impervious surface observed for each polygon in the LULC coverage; ISACRES, number of acres of impervious surface in each polygon calculated using IS.

The recharge (combination or cmb) coverages were created by overlaying each of the previous coverages in a specific order. The soil coverage was combined with the municipality coverage so that the county boundary was preserved. Then this coverage was combined with the LULC coverage. Once again the county boundary was preserved. Because the recharge model is recommended for areas of 5 acres or less, after each combination, the resultant coverage was generalized to 5 acres using the Arc/Info eliminate command. Not all polygons of less than 5 acres were eliminated resulting in some smaller polygons, especially along the edges of the coverage. Also, each constituent coverage may not have exactly matched in there geographic extent. This may have led to polygon slivers at the edges of very small sizes for which no recharge was calculated. In the interest of timely delivery, these polygons were not removed. Once the preliminary combination coverage was created, extraneous items were trimmed from the INFO PAT. Items retained were those deemed necessary for calculation of ground-water recharge. The items for the final combination coverages are: POLYID, unique polygon id number; MUNNAME, municipality name; COUNTY, county name; CF, climate factor; SYMBOL, soil series symbol; SERIES, soil series name; HYD, hydric soil indicator; LULC (renamed from MAJOR the NJGS LULC major category code), CF, climate factor and DCF, drought climate factors.

Calculation and ranking of ground-water recharge was done by converting the PAT data to spreadsheet file. Five items or columns were added to the file: GWR (ground-water recharge), INCH (gwr in in/yr), DGWR (drought ground-water recharge), DINCH (drought gwr in in/yr), CRANK or WRANK (county or WMA recharge rank indicator). Initially all hydric soils were identified (Y in the HYD item) and assigned the rank of “L” Next, wetlands and open water were identified (101 in LULC item and/or Water in SERIES item). These were given the ranking of “W”. All items which did not have either a SERIES or CF were then given a rank of “X”. Some of these have no soils mapped. They include: heavily urbanized areas such as Trenton, Camden, and northeast New Jersey cities; mine tailings dumps; and areas of unknown soil type. Other areas represent slivers of produced during processing of the three constituent coverages. Unranked items were then filtered out and copied to a new worksheet. There two more items were added-RF (rfactor) and RC (rconstant). These items were looked up from another spreadsheet using the SERIES and LULC item. The GWR and DGWR items were then calculated by this formula: (CF*RF)-RC and (DCF*RF)-RC respectively. The INCH and DINCH items were calculated by rounding the GWR and DGWR items, respectively, to the nearest integer. The CRANK or WRANK (C/WRANK) item was populated using the volumetric ranking method described in GSR-32.

The recharge data were summarize by summing the areas for each INCH category. Volumes were calculated for each INCH category and percentages of total volume were calculated. The 5 ranks were based solely on the 0 in/yr Category and on 4 significant data breaks identified in the data. Once the rank for each INCH category was determined, the RANK item was populated by a lookup against the INCH item to the rank summary table. The GWR, INCH, DGWR, DINCH and C/WRANK items were then propagated back to the original worksheet via a lookup using the polygon id item: POLYID.

Once all items were filled, an upload worksheet was prepared consisting of the POLYID, RF (rfactor), RC, GWR, INCH, DGWR, DINCH and C/WRANK items. This upload was then saved in dBase IV format (DBF file) and uploaded to Arc/Info where it was converted to an INFO data file, and matched by POLYID to the combination coverage which added the GWR, INCH DGWR, DINCH, and C/WRANK items to the recharge combination coverage. The GWR and DGWR items hold the calculated average and drought ground-water recharge in decimal inches/year (2 decimal places). The INCH and DINCH items are the GWR and DGWR items rounded to the nearest inch/year and the C/WRANK item holds the county or WMA-wide recharge rank indicator (A, B, C, D, E, L, W, or X) and finally, SRANK, added in ArcInfo, holds the statewide recharge rank (A, B, C, D, E, L, W, or X).

Recharge rank ranges are unique for each WMA, county and statewide, except the 0 in/yr category which is always "E", hydric soils are ranked "L", wetlands are ranked "W" and areas of no recharge calculations are ranked "X". The other ranks by county and statewide are as follows: